Communication system



Feb. 9, 1937.

w. A. KNooP COMMUNICATION SYSTEM Filed July 2l, 1935 l llmwjvll. Il

A \S \S UV T Y 9,.

/NVE/vroR W. A. KNOOP BV W/ ATTORNEY Patented Feb. 9, 1937 UNITEDOFFICE'- COMMUNICATION SYSTEM Application July 2l, 1933, Serial No.681,482

o 6 Claims.

This invention relates to electrical communication systems and moreparticularly to composite loaded communication systems forsimultaneously transmitting both telegraph and telephone messagecurrents.

In electrical communication cables it may be necessary to load the cableby winding a tape of magnetic material about the conductor or insertingloading coils having cores of magnetic material. This loading reducesthe ,attenuation of the cable to electrical currents, but due to thecharacteristics of the magnetic materials the signals are modulated anddistorted. In addition, in composite systems, the modulation products ofone set of currents may disturb the other sets of currents. This effectis greatest when the transmission of one set of currents (say thetelephone currents) is in one direction and the transmission of theother set, (the telegraph signals in this case), is in the oppositedirection.

Filters are usually employed to separate telephone and telegraphcurrents which lie in diierent frequency ranges but the filters areunable 'to attenuate those modulation products which have the samefrequencies as the desired currents selected by the filters.

The object of this invention is to provide means for preventing thetelegraph currents from modulating the telephone currents and at thesame time to balance the modulation products of the telephone currentsout of the telegraph receiving apparatus.

A feature of the invention is that the cable conductor is loaded in sucha manner that telephone channel is effectively loaded while thetelegraph channel is effectively non-loaded, so that telegraph messagecurrents may be transmitted in both directions simultaneously withtransmission of telephone message currents in either direction over thecable.

A further feature of the invention is that the loading is accomplishedby loading coils and disturbances due to the Barkhausen effect in themagnetic material of the loading coil due to the telegraph currents arebalanced out of the tele phone channel.

These objects are accomplished in one specific embodiment of theinvention to a deep sea submarine cable by providing special shore endsections to the cable having a telephone seavearth conductor or cableand a telegraph seaearth'conductor or cable in addition to the maincable or conductor. The main cable conductor and the telephone sea-earthconductor are providedl with loading coils having mutual inductancesbetween them. The telegraph circuit is then taken from the midpoint ofthe main cable and the telephone sea-earth cable and the telegraphsea-earth cable.

In order that the invention may be more fully understood two embodimentsof the invention will now be described in connection with the attacheddrawing in which:

Fig. l illustrates one embodiment of the invention as applied to asubmarine cable and,

Fig. 2 illustrates another embodiment of thek invention in which thetelegraph circuits which include a transmitting circuit, a receivingcircuit, the artificial line circuit and the telegraph seaearth circuitare shown in detail.

Referring now to Fig. 1, the portion I of the main deep sea cable ispreferably continuously loaded, but need not be. Connected to each endof cable l is a shore-end or terminal section as illustrated in Fig. lwhich is loaded with loading coils 'l having windings 5 and 6.Non-loaded i cable sections 2 and l which are connected between loadingcoils l may be the conductors or cores of twin core cables or twoindividual core cables. Conductors or cable sections 2 are connected inseries with the windings 5 of the loading coils 'l and the main deep seacable I. Cable sections 4 are connected in series with windings 6 ofloading coils 1 and the telephone sea-earth or balancing earth through acable '30 section 3 which is preferably similar in construction to cablel and may extend a considerable distance beyond the loading coil mostdistant from the shore. Connected to the shore-end of the cable sections2 and l closest to the shore 35 is the primary winding I3 of a telephonetransformer Il which is center tapped. The second- .ary winding l2 oftransformer Il is connected to the telephone iilters and switchingcircuits while the center tap of primary winding I3 of 40 transformer ilis connected to the telegraph transmitting and receiving circuit throughthe telegraph low pass filters.

The shore-ends of the cable, are coil loaded so that mutual coupling ispro-vided between the main cable and the sea-earth cable. It should benoted that the coils 5 and t are so connected to the main cableconductor and the sea-earth cable conductor so that they are seriesaiding for the telephone current, but series opposing for the telegraphcircuit.

Now let us consider what will happen in the rst loading coil. Thetelephone current from the primary winding i3 of transformer Iltraverses winding 5 of the first loading coilA 1, ows 55 through thecable to ground, back through the c telephone sea-earthconductor and theother winding 6 Vof the rst loading coil ltothe pri- `mary winding I3 oftelephone transformer II.

If the iterative irnpedancesA Ze andZs ofthe main cable conductor Yand.the sea-earth con-V ductor from points I1 and I8 to earth-respectivelyare equal and the windings 5 and 6 ofY loading coilV 1 areV identical,the midpoint of the primary I3 of transformer II will remain at earthpotential during the reception and transmission of the telephonecurrents. Y

However Vdue to the characteristics of the magnetic loading material ZtYand ZS vary with the current flowing in the cable. This causes harmonicvoltages or modulationproducts to be induced in the loading coils or inloaded conductors. A more detailed description of this type ofdistortion, modulation products and harmonic voltages may be found in anarticle Harmonic provductionin ferromagnetic materials by E. Petersonpublished in the Bell System Technical JournaL'vol. VII, pp. V762-796for October 1928.

By vwinding the coils connectedk in the two conductors on the same coreZC and'Zs will Vary in the same manner and vamount if the two windingsare identical and the modulation products or harmonic voltages will beequal in both coils and also have the same relative phase so thatvoltages will not appear at the center point of winding I3 oftransformer II. Y Y

'.If there is no mutual coupling between the windings'E and 8 of theloading coils 1 or if the conductors 2 and 4 are continuously loaded bywrapping tape about them n'ot only must Zc and ZS be equal, but themodulation products which e are generated in each conductor due tomagnetic loading material must be equal at each point along the cableand also be generated at the same phase at each point along the cable ifthe center tap of the primaryr winding I3 of the telephone transformerII is to remain at ground potential during the transmission andreception of the telephone currents. Since it is impossible tomanufacture loaded conductors suiiiciently alike to meetthese'requirements the advantage of a coil loaded shore sectionrinwhichthe same mag-V netic material is employedl to load both the main cableandthe sea-earth cable becomes quite apparent.

, Furthermore, since coils 5 and 6 are wound on the same core and areconnected in series opposition to the telegraph currents no Barkhauseneffects are produced in the telephone channel. Also since the coils areconnected in series opposing for the telegraph current, these currentswill produce no magnetic effects in the cores of the loading coils sothat the Vtelegraph currents are unable to Vmodulate the telephonecurrents or to produce any harmonics in these cores which Y mightdisturb the'telephone current.

Y Since the telegraph currents traverse the windings 5 and 6 in opposingdirections, this shore section of the cable is effectively unloaded withvided which is connectedV through cable sectionsV 4'8 to thetelegraph-articialfline andrtransmiti ting apparatus.

InY this case as in Fig. 1, cable Y sections 2, 4, anda are non-loadedand may be its individual cables orV may beconductors or cores in atriple core cable or conductors `2 and 4 may bein a twin core cable land8 in an individual v unnecessary to provide variable inductances in'the` artificial line which istherefore'much easier to construct andmaintain. However, it is necessary to include inductance elements whichcorrespond to the in ductance elements of the loaded mainV cable I asshown in sections I6 of the articial line. However, since there isappreciable attenuation in the initial sections I5 corresponding to thenon-loaded shore section, changes in the value of these inductances `orin the value of the inductance of the loaded cable do not appreciablyaffect the balance of the bridge I4 of the telegraph circuit. Y

While the drawing and above description disclose two specic embodimentsof the invention, it is to be understood that they are 'not to limit thescope of the invention as defined in the appended claims. I

What is claimed is: Y

l. A communication system for simultaneously transmitting voicefrequency telephone message currents and low frequency telegraph messagecurrents comprising a main cable section, terminal cable sectionsconnected to the ends of said main cable section, said terminal cableshaving` currents between said telegraph balancing earth conductor andthe midpointrof said telephone 1.

transmitting .and receiving means.

2. A submarinecommunication system for simultaneously transmitting voicefrequency tele-` phone message currents and low frequency telegraphmessage Vcurrents comprising a main cable section and terminal cablesections connected to the ends of said main cable section, characterizedin this that said terminal cable sections comprise ductor and atelephone sea earth conductor.

3. A communicationV system comprising a main va main conductor,atelegraph sea earthr conf loaded single conductorcable,terminalsectionsV connected to the ends of said main cablecomancing sea earth conductor, a telegraph balancing sea earthconductor, loading coilshaving a` coil connected in series with Vsaidmain cable conductorrand anotherccoil connected in series with saidtelephone sea earth conductor ysaid coils hav.-

ing mutual inductancefbetween them, and means y,for transmittingandreceiving telephonersignal currents to and from said main cablesection and said telephone sea earth conductor, and means fortransmitting-and receiving telegraph current to and from said telegraph,sea earth conductor andthe midpoint between said'main conductor Y andsaid telephone sea earthconductor;`

4..A composite deep sea communicationsys-A ltem for simultaneouslyAtransmitting and receiv' ing telegraph and telephone signal currentswhich comprises -a main loaded cable, short cable sections connectedthereto having a main conductor and a telephone sea earth conductor,loading coils for loading said conductors for telephone currents havingtwo windings mutually coupled together, one of the windings of each ofsaid loading coils being connected in series with said main conductorand the other of said windings of each of said coils being connected inseries with said telephone sea earth conductor, and means for applyingsaid telephone signal currents between said conductors and additionalmeans for applying said telegraph currents to said conductors equallyand to ground.

5. A deep sea communication system comprising a deep sea cable section,a shore cable section connected to the ends of said deep sea cablesection, said shore cable section comprising a main conductor, atelephone sea earth conductor and a telegraph sea earth conductor,loading coils having two windings mutually coupled together, one ofwhich is connected in series with said main conductor, the other Windingof which is connected in series with said telephone sea earth conductor,and means for simultaneously transmitting and receiving voice frequencytelephone message currents and low frequency telegraph message currentsconnected to the conductors of said shore cable section whereby theinductance for said telephone currents is increased but the inductanceto said telegraph currents is not increased.

6. A deep sea communication system for simultaneously transmitting andreceiving both Voice vfrequency telephone message currents and lowfrequency telegraph message currents, comprising a deep sea cablesection, shore cable sections connected to the ends of said deep seacable section, said shore cable sections comprising a main cableconductor, a first sea earth conductor and a second sea earth conductor,a plurality of loading coils having two windings mutually coupledtogether one of which is connected in series with said main conductorand the other of which is connected in series with said rst sea earthconductor, means for transmtting'and receiving one of said messagecurrents to said main conductor and said rst sea earth conductor, andmeans for transmitting the other of said message currents equally oversaid main cable conductor and said first-mentioned sea earth conductorand over said second sea earth conductor.

WILLIAM A. KNOOP.

